fix(signals): remove signalMethod instance watcher on destroy (#4648)

Closes #4644

modules/signals/spec/signal-method.spec.ts

@@ -72,18 +72,15 @@ describe('signalMethod', () => {
       const adder = createAdder((value) => (a += value));
       adder(summand1);
       adder(summand2);
-
-      summand1.set(2);
-      summand2.set(3);
       TestBed.flushEffects();
-      expect(a).toBe(6);
+      expect(a).toBe(4);
 
       adder.destroy();
 
       summand1.set(2);
       summand2.set(3);
       TestBed.flushEffects();
-      expect(a).toBe(6);
+      expect(a).toBe(4);
     });
 
     it('does not cause issues if destroyed signalMethodFn contains destroyed effectRefs', () => {
@@ -198,4 +195,23 @@ describe('signalMethod', () => {
       expect(a).toBe(5);
     });
   });
+
+  it('stops specific tracking when calling destroy manually on an instance', () => {
+    let a = 1;
+    const summand1 = signal(1);
+    const summand2 = signal(2);
+    const adder = createAdder((value) => (a += value));
+    adder(summand1);
+    const s2 = adder(summand2);
+
+    TestBed.flushEffects();
+    s2.destroy();
+    expect(a).toBe(4);
+
+    summand1.set(100);
+    summand2.set(3000);
+
+    TestBed.flushEffects();
+    expect(a).toBe(104);
+  });
 });

modules/signals/src/signal-method.ts

@@ -1,5 +1,6 @@
 import {
   assertInInjectionContext,
+  DestroyRef,
   effect,
   EffectRef,
   inject,
@@ -35,15 +36,21 @@ export function signalMethod<Input>(
         config?.injector ?? getCallerInjector() ?? sourceInjector;
 
       const watcher = effect(
-        (onCleanup) => {
+        () => {
           const value = input();
           untracked(() => processingFn(value));
-          onCleanup(() => watchers.splice(watchers.indexOf(watcher), 1));
         },
         { injector: instanceInjector }
       );
       watchers.push(watcher);
 
+      instanceInjector.get(DestroyRef).onDestroy(() => {
+        const ix = watchers.indexOf(watcher);
+        if (ix !== -1) {
+          watchers.splice(ix, 1);
+        }
+      });
+
       return watcher;
     } else {
       processingFn(input);